Patent GB-1343479-A (GB)
Title: Control rod drive for a nuclear reactor
IPC: G21C7/16
Filed: 1971-06-07
Abstract: 1343479 Controlling reactors LICENTIA PATENT-VERWALTUNGS GmbH 7 June 1971 [6 June 1970 11 Aug 1970 30 Sept 1970 8 May 1971] 19274/71 Heading G6C A control rod drive for a nuclear reactor comprises two control pistons located in a guide tude, each piston being provided with locking elements for holding it stationary, and means for causing the locking elements to lock the pistons alternately, one piston remaining locked stationary when the other piston is moving. The drive shown in Fig. 1 is located in the reactor pressure vessel beneath the core grid plate and comprises a guide tube 1 in which slides a piston 2 on which the control rod (not shown) is mounted. The piston 2 is seated on an upper control piston 3 which has an interlocking arrangement 4 which can engage in notches 5, 5<SP>1</SP>, 5<SP>11</SP> ... in the guide tube 1 and thus prevent downward movement of the upper control piston 3. A second control piston 6 is located beneath the control piston 3 and has an interlocking arrangement 7 constructed in the same way as the arrangement 4. These arrangements 4, 7 each consist of two detents 8, 9 pressed apart by means of springs 10 and so shaped that upon upwards movement of the lower control piston 6, they slide out of the notches, sliding into them in the event of a downwards movement. On its underside, the upper control piston 3 has two dogs 11, 12 which fit into slots 13, 14 on the detents 8, 9, which slots have chamfers 15, 16 so that the detents 8, 9 are moved radially out of the relevant notches by the dogs 11, 12 moving into the slots 13, 14. The lower control piston 6 has an extension 17 which penetrates the upper control piston 3 and has at its upper end a top piece 18 with dogs 19, 20 which correspond to the dogs 11, 12 and can likewise move into slots in the upper interlocking arrangement 4. Pipe connections (not shown) ensure that a somewhat higher hydraulic pressure acts on the upper side of the upper control piston 3 than on the upper side of the lower control piston 6. A particularly advantageous actuating circuit is described with reference to Fig. 5 (not shown). Assuming the reactor pressure to prevail at the bottom of the guide tube 1, then an increased pressure in the space above the upper control piston 3 will first move the unlatched upper control piston 3 downwards on to the lower control piston 6 whereupon the interlocking arrangement 4 engages in the notch 5<SP>1</SP> and locks the piston 3. The piston 2 drops by the same amount together with the control rod. The dogs 11, 12 move into the slots 13, 14 of the lower control piston 6 which is thereby released. If the working pressure is now reduced beneath the lower control piston 6 or increased above it, then it travels downward as far as the next lower notch. As soon as it is engaged therein, the dogs 19, 20 of the top piece 18 release the upper control piston 3 which can again perform a downwards movement as described above. A fast shut-down or scram is effected either by supplying an increased pressure under the pistons 3, 6 (active fast shut down) or by releasing pressure from above the pistons (passive fast shut down) as is described with reference to Figs. 5 and 6 (not shown). The control rod has a cruciform absorber portion 751 (Fig. 8) formed with four wings 752, 752<SP>1</SP>, 752<SP>11</SP>, 752<SP>111</SP> joined at the top and provided with vertically-directed slots to enable them to engage over the guide tube 1.